Process for the low temperature carbonization of bituminous coal



Feb. 5, 1963 R. c. MINET {A 3,076,751 PROCESS FOR THE LOW TEMPERATURECARBONIZATION OF BITUMINOUS COAL Filed Aug. 27, 1959 CHAR ' IN V EN TOR.flaw/u 0 6 M/A/U United States Patent "Ofilice 3,076,751 Patented Feb.5, 1963 3,076,751 PROCESS FUR THE LBW TEMPERATURE CAR- BQNEZATIQN FBITUMINOUS COAL Ronaid Minet, Philadelphia, Pa., assignor to UnitedEngineers & Constructors lno, Phiiadeiphia, Pa. Filed Aug. 27, 1059,Ser. No. 836,524 5 Claims. (Cl. 202-9) This invention relates to aprocess for the carbonizetion of bituminous coal at low temperature andparticularly to a process whereby such carbonization can be carried outin a fluidized bed without a preoxidation step.

Many attempts have been made to develop an economical process for thecarbonization of bituminous coal at temperatures below about 1000 F. Insome countries, such processes are economically feasible and are in use.In the United States however, so far as is known, no such process is nowin commercial operation.

In recent years a number of proposals have been made with a view towardadapting the fluidized bed technique to low temperature carbonizationprocesses. In most of such proposals however, the coal having beenreduced to finely divided form must first be preoxidized to keep it fromagglomerating when heated to carbonization temperatures. This hasrequired a minimum of two fluidized beds, one for preoxidation andanother for carbonization.

This arrangement is inherently costly, since the gaseous stream removedoverhead from the preoxidation bed consists very largely of products ofcombustion, which have little value. In no case is more than say 50% ofthe recoverable tar recovered during the preoxidation. Thus the majorcost of building, maintaining and operat ing a fluidized bed preoxidizeris necessary simply to prepare the coal for car-bonization.

It is an object of the present invention to provide a process for thelow temperature carbonization of certain bituminous coals in which nopreoxidation step is necessary.

It is a further object of the present invention to provide a process forthe low temperature carbonization of certain bituminous coals using thefluidized bed technique in which only one fluidized bed is necessary.

It is another object of the invention to provide a process for thecarbonization of certain bituminous coals which will be more economicalthan existing processes.

According to the invention these and other objects are obtained byheating certain widely distributed types of bituminous coal at acarefully controlled temperature between about 800 F. and about 840 F.It has been found that by heating at this temperature the dry volatilecontent of the coal can be reduced to between about 18% and about 26% byweight, without danger of agglomeration, in a fluidized bed. Suchtreatment enables a mini mum of 70% by weight of the tars and oils whichit is possible to derive from the coal by carbonization, to be recoveredin a single step. If desired, the remaining tars and oils may berecovered 'by further heating in a second stage at say 860 to 1600 F.

It should be pointed out that the amount of volatile matter which can berecovered from a particular coal is a function of temperature, i.e. forany particular coal the volatile content which will remain in the coalafter it has been heated to a given temperature is fixed. For most ofthe coals covered by the present process a minimum temperature of 800 F.is necessary in order to reduce the volatile content to 18-26% andrecover a minimum of 70% of the tar.

Coals which can be treated according to the present invention are amongthose designated High Volatile B Bituminous (HVBB) and High Volatile CBituminous (HVBC) according to the ASTM classification by rank. Suchcoals contain less than 69% dry fixed carbon and more than 31% dryvolatile matter. They have a moist heating value between about 11,000and about 14,000 B.t.u. per pound. For a description of the ASTM andother systems of classification, see Lowry, Chemistry of CoalUtilization (John Wiley and Sons, New York, 1945), chapter 2. HVBB andHVBC coals are widely distributed throughout the United States and arefound in Pennsylvania, West Virginia, Kentucky, Ohio and Illinois. Suchcoals are particularly distinguished by the proportion of moisture andash free oxygen present in the ultimate analysis. Coals which areamenable to treatment of the kind described contain at least 4 percentand preferably 6 to 12% by weight of oxygen on a moisture and ash freebasis.

In carrying out the invention, the coal is preferably first reduced to aparticle size to between about 4 mesh and about 325 mesh, usuallybetween about 8 mesh and about 325 mesh. The imely divided coal is thensuspended in a fluidized bed in a suitable reaction vessel equipped witha gas distributing device. Heat may be supplied to the bed by anyconvenient means, as for example by hot gases, which may also serve as afluidizing medium. These gases may be entirely inert, such for exampleas steam or nitrogen, or they may contain quantities of oxygen or air.In the latter instance, the oxygen or air is used to burn a portion ofthe suspended coal to furnish at least part of the heat ofcarbonization.

The char resulting from the carbonization may be removed from the bedand further treated to recover the balance of the volatile matterremaining in it. This further recovery may be obtained by delivering thefinely divided char to a second fluidized bed and heating it to above860 F. and preferably not higher than 1600 F. to further reduce thevolatile content.

The invention will be further described in the drawings in which FIG. 1is a schematic flow diagram showing a preferred form of a carbonizationsystem according to the invention, and

FIG. 2 is a schematic representation of another system according to theinvention in which coal can be carbonized at a relatively lowtemperature and then further distilled at a higher temperature to removeresidual volatile matter.

Referring first to FIG. 1, coal is fed into a mill 1 where it is reducedto a particle size in the range between about 10 mesh and about 325mesh. Thus divided, it iscarried to a carbonization vessel 2 through aline 3. At the same time a fluidizing gas is fed into the vessel througha line 4 to form a fluidized bed 5, in the vessel 2. A grid 6 isprovided at the bottom of the vessel to sustain the fluidized bed. Thegas, introduced through line 4, may be an inert gas such for example assteam, or a mixture of an inert gas and an oxidizing gas, such forexample as a mixture of steam and air. If steam is introduced alone, itshould be at a temperature between about 1000 F. and about 1400 F. sothat the temperature in the bed is maintained between about 800 F. andabout 840 F. if a mixture of an inert gas and oxygen is introduced, itmay be preheated, as for example to between about 600 F. and about 800F., or it may be introduced at the ambient temperature. The proportionof oxygen present in the gas will depend on a number of factors,including the dimensions and design of the reactor, the size of the coalparticles, the rate of coal processed and of course, the temperature towhich the bed must be heated. When used, oxygen will generally comprisebetween about 10% and about 15% by volume of the fiuidizing gas.

At a temperature between about 800 F. and about 840 F., coal of theclass described, containing over 31% dry volatile matter, distills,giving off a mixture of tars, oils and gases. The tars and oils areoften referred to merely as tars. These volatile products pass outthrough a cyclone separator 7 and are removed from the system throughline 8. They may then be separated into salable components bydistillation or other means not shown. Char is removed through a line 9at the bottom of the vessel 2.

As noted, the char removed from a carbonization vessel operatedaccording to the invention contains a residue of between about 18% andabout 26% by weight dry volatile matter. Whether it will be worthwhileto remove all or par-t of this residue depends on the composition of theparticular coal and of the residue.

With certain HVBB and HVBC coals it may be economically justifiable tofurther carbonize at a temperature as high as 1600" F. in order toobtain a maximum yield of gaseous and liquid products.

A suitable system for carrying out the novel process where removal ofthe residual 18 to 26% volatile matter is desired, is shown in FIG. 2.Referring to FIG. 2, coal finely divided to a particle size betweenabout inch and about 325 mesh, preferably to between about /8 inch andabout 325 mesh, is introduced through a line 10 into a first carbonize-r1.1. A fiuidizing gas is introduced at the bottom of the carbonizer 11through a line 12. This creates a fluidized bed 13 which is supported ona grid 14 at the bottom of the vessel 11. The fiuidizing gas introducedthrough line 12 may be an inert gas, or a mixture of an inert gas and anoxidizing gas, as described in connection with FIG. 1 above. As in FIG.1, the bed 13 is heated to between about 800 F. and about 840 At thistemperature a large portion of the volatile material present in the coalpasses overhead through cyclone separator 15 and line 16, and is thenceremoved from the system.

The solid residual char containing 18 to 26% volatile matter is removedfrom the vessel 11 through an overflow trap 17 into an inclined duct 13.Here it flows through a valve 19 into a second carbonizing vessel 20where it is formed into a fluidized bed 21 supported on a grid 27, bymeans of a hot fluidizing gas introduced through a line 22.

The fiuidizing gas used in the bed 21, like that used in bed 13, and inthe fluidized bed of FIG. 1, may be an inert gas, such as steam or amixture of an inert gas and anoxidizing gas, such as a mixture of steamand air. In the latter case, the oxygen supports combustion of a portionof the char formed in the carbonizer 20 and thus serves to heat the bed21.

When no oxygen is present in the gas introduced through line 22, the gasshould be at a temperature between about 1240 F. and about 2000 F., sothat the bed is maintained at a temperature between about 860 F. andabout 1600 F., preferably between about 860 F. and about 1000 F.

When oxygen is used, the gas entering through line 22 may bepreheated,for example to a temperature between about 600 F. and about 900 F., orit may be introduced at ambient-temperature. The proportion of oxygen inthe gas will, as explained above, be governed by many factors includingthe dimensions and design of the vessel 20, the size of the coalparticles and the temperature desired in the bed 21. Generally it isbetween about 5% and about 10% by volume.

As pointed out, the temperature in the bed 21 is maintained betweenabout 860 F. and about 1600* R, preferably between about 860 F. andabout 1000 F. At these temperatures residual volatile matter is removedfrom the coal and passes overhead through cyclone separator 23 and line24 through which it is removed from the system.

The char remaining, which now contains between 5 and about 20% by weightdry volatile matter, is removed through standpipe 25 and line 26. It maybe used as a fuel, or for other purposes, such as for the production ofmetallurgical carbon.

The invention will be further described by means of the followingspecific examples, it being understood that these examples are given forpurposes of illustration only and are not to be taken as in any wayrestricting the invention beyond the scope of the appended claims.

In the examples five different types of high volatile B bituminous coalwere used. These types are designated A to E and are described in detailin Table I.

1 V111 =Volatile matter, percent by weight. 2 FO=Fixed carbon, percentby Weight.

Moist means that the coal contains natural bed moisture but not visiblewater on its surface.

Example I Two hundred pounds per hour of coal A were fed into afluidized bed of the same material maintained at a temperature of 830 F.Steam was used as the fluidizing gas, with sufiicient air beingintroduced to provide the necessary heat for carbonization by combustionof the char. A superficial gas velocity of 1.2 feet per second wasmaintained at the bottom of the bed. The following products wererecovered each hour from this operation:

Light oil 0.30 gallon. Tar 2.50 gallons. Gas 800 std. cu. it. at 350B.t.u./c.f. Char 140 pounds.

The char remaining contained 20% by weight dry volatile matter. Theproportion of total recoverable tar (tar and oil) actually recovered inthe single carbonization stage was about 90%.

Examples 11 to V Examples II to V are tabulated below in Table II. InExample V, the residual char from the first carbonization step wasfurther carbonized at the temperatures indicated using steam and air asthe heating and fluidizing medium.

TABLE II Example II III IV V Coal treated B O D E Coal iced rate,lbs/hr... 200 200 200 200 1st carbonization stage:

Fluidizmg and heating medium. Bed temp, F 800 820 800 800 Overheadproduct, lbs/hr]- 44. 2 7 1. 2 42. O '13. 2 Analysis, weight percent:

\Vat 41. 8 31. O 28. 7 .3 11. 3 9. 5 8. 'J .1 4. 2 7. 2 8. 0 .1 42. 752. 3 53. 5 Char:

Obtained, lbs/hr 147. 115.8 151. 2 146. 3 Loss, lbs/hr S. 0 10.0 6. 8 8.5 Weight percent dry volatile matter 23. 1 20.0 22. 8 22. 0 Percenttotal tar and light oil recovered 86. 0 81.0 71. 2 83. 0 2ndcarbonization stage:

Fluidizing and heating mcdium Bed temp, F 950 Overhead product, lbs/hr14. 0 Analysis, weight percent: 5

W" or 7. 3 Gas 43. 0 Light on 14. 6 Tar" 35.1 Char:

Obtained, lbs/hr 130.6 Loss, lbs/hr. 1. 3 Weight percent dry volatilematter 1'1. 1

1 Steam and air. 2 Steam. 8 All on air and steam free basis.

A consideration of the foregoing specification will make it clear thatthe present invention permits a number of common coals of theagglomerating type to be carbonized directly in a fluidized bed withoutoxidation pretreatment. It must be emphasized that the primarycarbonization stage of the present invention (which in most cases willbe the only carbonization stage) is a true carbonization step and notmerely a pretreatment, since in every case at least 70% of thepotentially recoverable tars and oils are distilled off in this step.

A distinction is therefore to be drawn between the present process andother carbonization processes using oxidation pretreatments. In suchprior processes, the temperature of the pretreatment may occasionally bequite high, but for any specific coal, the temperature will not besufiicient to recover more than at most 50% of the total recoverable tarand oils, and would therefore be considerably lower than the temperaturewhich would be used if the present process were applied to that coal.

In the foregoing specification coal is described as being furnisheddirectly to the carbonization vessel without preheating. It will beunderstood that if desired a certain amount of preheating may be carriedout to remove surface water. Such preheating will be below 400 F. andwill not in any way change the essential nature of the coal.

This patent application is a continuation-in-part of the Minet patentapplication, Serial No. 562,980, tiled February 2, 1956, now abandoned.

What is claimed is:

1. A method for the low temperature carbonization of a normallyagglomerating coal which consists essentially of charging a feed streamconsisting essentially of fresh finely divided coal having more thanabout 31% dry volatile matter and a moist heating value of between about11,000 and about 14,00 B.t.u./lb., into a fluidized zone maintained at atemperature between about 800 F. and about 840 F., and educinghydrocarbona ceous matter from said coal in said zone until at least 70%by weight of the total tars and oils initially present in the coal areremoved and the dry volatile content of said coal is reduced tobetween'about 18% and about 26% by weight without substantialagglomeration of said coal.

2. A method for the low temperature carbonization of a normallyagglomerating bituminous coal having more than about 31% dry volatilematter and a moist heating value of between about 11,000 and 14,000B.t.u./ 1b., which consists essentially of charging a feed streamconsisting essentially of fresh coal to a fluidized carbonization zoneat a temperature between about 800 F. and about 840 F. and maintainingsaid coal in said zone for a period sufficient to remove at least byweight of the total tars and oils initially present in the coal and toreduce the dry volatile content of said coal to between about 18% andabout 26% by weight, there being substantially no agglomeration in saidzone.

3. The method claimed in claim 2 and comprising burning a portion of thecoal in the fluidized zone to furnish heat for the carbonization.

4. A method for the low temperature carbonization of a normallyagglomerating bituminous coal having more than about 31% dry volatilematter and a moist heating value of between about 11,000 and about14,000 B.t.u./lb., which consists essentially of charging a feed streamconsisting essentially of fresh coal to a first fluidized carbonizationzone maintained at a temperature between about 800 F. and about 840 F.,maintaining said coal in said zone for a period suificient to remove atleast 70% by weight of the tars and oils initially present in the coaland to reduce the dry volatile content of said coal to between about 18%and about 26% by weight, and then feeding said coal to a secondfluidized carbonization zone at a temperature between about 860 F. andabout 1600 F. but higher than the temperature in said firstcarbonization zone, there being substantially no agglomeration in eitherzone.

5. The method claimed in claim 4 wherein the coal in the second zone isheated to between about 860 F. and about 1000 F.

References Cited in the file of this patent UNITED STATES PATENTSWelinsky May 4, 1954 Welinsky Oct. 4, 1960 OTHER REFERENCES

1. A METHOD FOR THE LOW TEMPERATURE CARBONIZATION OF A NORMALLYAGGLOMERATING COAL WHICH CONSISTS ESSENTIALLY OF CHARGING A FEED STREMCONSISTING ESSENTIALLY OF FRESH FINELY DIVIDED COAL HAVING MORE THANABOUT 31% DRY VOLATILE MATTER AND A MOIST HEATING VALUE OF BETWEEN ABOUT11,000 AND ABOUT 14,000 B.T.U./LB., INTO A FLUIDIZED ZONE MAINTAINED ATA TEMPERATURE BETWEEN ABOUT 800*F. AND ABOUT 840*F., AND EDUCINGHYDROCARBONACEOUS MATTER FROM SAID COAL IN SAID ZONE UNTIL AT LEAST 70%BY WEIGHT OF THE TOTAL TARS AND OILS INTIALLY PRESENT IN THE COAL AREREMOVED AND THE DRY VOLATILE CONTENT OF SAID COAL ARE REMOVED AND THEDRY VOLATILE CONTENT 26% BY WEIGHT WITHOUT SUBSTANTIAL AGGLOMERATION OFSAID COAL.